The invention relates in general to plastic bonded explosive molding powder and in particular to an improved coating process for plastic bonded explosive molding powder.
Traditional water slurry methods for producing explosive molding powder have been used for over 40 years in explosive production facilities. Even when a high quality molding powder is produced by the traditional water slurry method, uncoated explosive particles remain in the batch. These uncoated explosive particles damage the sensitivity characteristics of the explosive molding powder.
Plastic bonded explosive molding powder is typically made in a batch process. A polymer is dissolved in an organic solvent to form a lacquer. The lacquer is mixed with a high explosive solid in a slurry kettle filled with water. After the lacquer is transferred to the mixture, the temperature is raised to distil off the solvent. The slurry is cooled and the batch is dewatered and then dried.
In known coating processes, granulation of the molding powder occurs during the addition of the lacquer, or by the addition of quench water after addition of the lacquer, and it is very difficult, if not impossible, to uniformly coat all of the explosive material surface with binder. Therefore, there exists a need for a coating process that results in a more uniform coating of all sizes of explosive material particles.
The present invention provides a method of making a batch of explosive molding powder comprising preparing a lacquer comprising an organic solvent, a binder and, if required by the explosive formulation, a plasticizer; adding water to a kettle; adding explosive material to the kettle; adding the lacquer to the kettle; heating contents of the kettle to above 98 degrees C.; cooling the contents of the kettle to below about 55 C.; separating the water from the explosive material; and drying the explosive material to form the explosive molding powder.
Using the above method, the present invention ensures that granulation of the molding powder is delayed until some of the solvent is removed by evaporation and/or distillation, thereby ensuring that all the explosive particles are coated with binder.
The present invention can be used to manufacture, or rework, any of the explosive formulations made by traditional methods, the binder to plasticizer ratio being predetermined by existing explosive material specifications.
Preferably, the organic solvent comprises ethyl acetate or methyl ethyl ketone, the binder and the plasticizer are in accordance with the explosive specification and may be selected by those skilled in the art. A ratio of an amount of solvent to binder is in the range of about 24:1 to about 90:1. A ratio of an amount of water to explosive batch is in the range of about 4:1 to about 8:1, the preferred amount of water being dependent upon the size of granulation required for the molding powder.
The explosive ingredients and the lacquer are then added to a kettle and agitated. Depending upon the explosive formulation being produced, the agitation may occur at ambient temperature. However, for certain explosive formulations, an agitator speed, for example 45 rpm, is established prior to adding any material to the kettle. The explosive material is then added and agitated at ambient temperature for a time period which is dependent upon the explosive formulation. The kettle is heated to from about 53 degrees C. to about 62 degrees C. and higher agitator speed is then established, for example 70 rpm, and the lacquer is added to the kettle and the mixture is agitated for a time dependent upon the explosive formulation. For reworking batches, either for granulation and/or composition, the lacquer is added to the kettle at ambient temperature to prevent excessive deposits on the wall of the vessel.
The mixture is then heated to about 98 degrees C. for about 10 to about 30 minutes. The mixture is then cooled to below about 55 degrees C. During the cooling step, the agitator speed is slowed, for example to about 50 rpm. The mixture is then dried until explosive material moisture content is less than about 0.1%.
Further objects, features and advantages of the invention will become apparent from the following detailed description.
The present invention includes a new coating process for producing high coating quality molding powder. The presence of uncoated explosive particles is minimized as are batch-to-batch variations. Explosive molding powder produced by the invention showed the following advantages:
1. Better and more reliable coating quality.
2. A decrease in the amount of uncoated particles, particularly uncoated fine particles.
3. Improvement in safety characteristics because of eliminating or minimizing uncoated particles.
4. No dusting problem during pressing operations because of eliminating or minimizing uncoated fine particles.
5. More reproducible, simpler manufacturing process with a lower reject rate.
6. More consistent material characteristics, such as bulk density and powder internal frictional coefficient.
The inventive process includes the following steps:
1) The first step in the process of making explosive molding powder is to make a lacquer. The lacquer for coating explosive molding powder is a mixture of an organic solvent, a binder and if required, a plasticizer. The ratio of the amount of solvent to binder is in the range of about 24:1 to about 90:1. The solvent is poured into a first kettle having an agitator. The binder and plasticizer are added and the ingredients are agitated until the binder has dissolved.
2) The second step in the process is to add water. The water is added to a second kettle with an agitator. The second kettle includes a steam, or oil heating jacket, and a condenser system such that the organic solvent may either be refluxed or distilled. The water to batch ratio is in the range of about 4:1 to about 8:1. xe2x80x9cBatchxe2x80x9d is defined as the amount of explosive material plus the amount of binder plus the amount of any required plasticizer.
3) The required amount of explosive material is added to the water in the second kettle and agitated at ambient temperature (around 23 degrees Centigrade) for about 10 minutes to about 30 minutes dependent upon the explosive formulation. Numerous explosive materials can be used in this process, for example RDX (Cyclotrimethylenetrinitramine) or HMX (Cyclotetramethylenetetranitramine), and can be selected by those skilled in the art.
4) If required for the explosive formulation, the vessel is heated to from about 53 degrees C. to about 62 degrees C. This brings the temperature of the slurry in the second kettle to from about 50 degrees C. to about 64 degrees C.
5) The lacquer is added over from about 10 minutes to about 30 minutes to the second kettle at a temperature from about ambient to about 65 degrees C. and the slurry is then agitated for about 30 to about 60 minutes.
6) The slurry in the second kettle is slowly heated until the temperature is greater than 98 degrees C. Granulation of the explosive material is achieved during this heating step.
7) The temperature is maintained above 98 degrees C. for about 10 to about 30 minutes to finish distilling off the solvent.
8) The slurry is then cooled to below about 55 degrees C.
9) The water is separated from the explosive material by, for example, discharging the slurry through a valve in the bottom of the kettle and filtering the slurry to remove the explosive material.
10) If desired, the explosive material may be washed with water to remove any remaining solvent.
11) The explosive material is placed in trays and dried in an oven until the moisture content is less than about 0.1%.